Class CNS
- java.lang.Object
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- org.jcsp.net.cns.CNS
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public class CNS extends java.lang.Object implements Service, CSProcess
This class is the Channel Name Server's main server process class.
This class should only be instantiated at Nodes wishing to run a server process. Although this class does not need to be used by clients wishing to interact with a server, it does provide some convenient static methods for client code to use. There are static versions of the methods provided in
CNSService
and there are also static factory methods for constructing CNS registered channel objects.Server Installation
Channel Name Servers may be run either on a dedicated Node or else on the same Node as one of the user Nodes. The former approach is recommended for most sitations but for smaller scale use, the latter approach may suffice. The service implements the
org.jcsp.net.Service
interface and can be installed in the same way as any other other service by using the service manager (ServiceManager
). Alternatively, the service provides install methods which handle the service manager interaction directly.The following example initializes a Node and installs a Channel Name Server. It then proceeds to install a CNS client service and creates and resolves a channel. The example does not proceed to do anything else but could be used as the framework for an application wishing to host its own Channel Name Server.
import org.jcsp.lang.*; import org.jcsp.net.*; import org.jcsp.net.cns.*; import org.jcsp.net.tcpip.*; import java.io.IOException; public class CNSInSameJVM implements CSProcess { //main method for running example public static void main(String[] args) { CNSInSameJVM proc = new CNSInSameJVM(); proc.run(); } public void run() { NodeKey key = null; NodeID localNodeID = null; try { //Initialize a Node that does not have a CNS client key = Node.getInstance().init(new XMLNodeFactory("nocns.xml")); localNodeID = Node.getInstance().getNodeID(); //Initialize the CNS Server Process CNS.install(key); //Dedicated server code could stop here //Initialize the CNS client //use the first address of the local Node as CNS address NodeAddressID cnsAddress = localNodeID.getAddresses()[0]; CNSService.install(key, cnsAddress); //creating Channel named "in" NetChannelInput in = CNS.createNet2One("in"); //resolve the channel NetChannelOutput out = CNS.createOne2Net("in"); //could now use these channels for something!! //but this is only a test so will terminate } catch (NodeInitFailedException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } Node.info.log(this, "Done."); } }
This is the contents of the nocns.xml file:
<JCSP-CONFIG>
<PROTOCOLS>
<PROTOCOL id="TCPIP" name="TCP/IP" idclass="org.jcsp.net.tcpip.TCPIPProtocolID">
</PROTOCOL>
</PROTOCOLS>
<ADDRESSES>
<ADDRESS protocolid="TCPIP" value="127.0.0.1:7896" unique="FALSE">
</ADDRESS>
</ADDRESSES>
</JCSP-CONFIG>
The above code can be copied into a file named CNSInSameJVM.java and compiled an run in same directory as the nocns.xml file.
Channel Factory Methods
In order to construct a
ChannelInput
object which can be resolved by other users of a channel name server, a client simply needs to to do this:NetChannelInput in = CNS.createNet2One("Fred");
Another process using the same channel name server can create a
ChannelOutput
that will send objects to this channel by do this:NetChannelOutput out = CNS.createOne2Net("Fred");
When these factory methods are called, various resources are used within the JCSP infrastructure. A channel name will be registered and held in the channel name server. These resources are taken for the duration of the JCSP Node's runtime unless the user manually frees the resources. When channel ends are constructed with these factory methods, the
destroyChannelEnd(***)
methods can be used to free all resources. It is only really necessary to do this if channels are being created for short term use within a long-lived Node.This is an example "Hello World" program which contains two inner classes with main methods, each of which can be run in separate JVMs.
import org.jcsp.lang.*; import org.jcsp.net.*; import org.jcsp.net.cns.*; public class TestCNS { public static class Rx { public static void main(String[] args) { try { Node.getInstance().init(); NetChannelInput in = CNS.createNet2One("rx.in"); System.out.println(in.read()); CNS.destroyChannelEnd(in); } catch (NodeInitFailedException e) { e.printStackTrace(); } } } public static class Tx { public static void main(String[] args) { try { Node.getInstance().init(); NetChannelOutput out = CNS.createOne2Net("rx.in"); out.write("Hello World"); CNS.destroyChannelEnd(out); } catch (NodeInitFailedException e) { e.printStackTrace(); } } } }
This code can be compiled and then the following run at two command prompts:
java TestCNS$Rx
java TestCNS$Tx
The programs will connect to a default channel name server. The Rx program will create a
NetChannelInput
and wait for a message on the channel. Once it has received the message, it prints it, destroys its channel and then terminates. The Tx program creates aNetChannelOutput
that will send to the Rx program's input channel. It sends a "Hello World" message. Once this has been accepted by the Rx process, it destoys its output channel and terminates.CNS Client Methods
The following code functions the same as the above code but does not use the CNS class' factory methods. The code uses the CNS client methods and manually registers and resolves the channel with the channel name server.
import org.jcsp.lang.*; import org.jcsp.net.*; import org.jcsp.net.cns.*; public class TestCNS { public static class Rx { public static void main(String[] args) { try { Node.getInstance().init(); NetChannelInput in = NetChannelEnd.createNet2One(); ChannelNameKey key = CNS.register(in, "rx.in"); System.out.println(in.read()); CNS.deregisterChannelName("rx.in", null, key); } catch (NodeInitFailedException e) { e.printStackTrace(); } } } public static class Tx { public static void main(String[] args) { try { Node.getInstance().init(); NetChannelLocation loc = CNS.resolve("rx.in"); NetChannelOutput out = NetChannelEnd.createOne2Net(loc); out.write("Hello World"); out.destroyWriter(); } catch (NodeInitFailedException e) { e.printStackTrace(); } } } }
The CNS client methods provide the programmer with greater control over how the Channel Name Server is used. Interaction with the server need not be performed at the same time as construction of the channel. A channel can be registered with a Channel Name Server at any time after construction of its input end. A channel can be resolved at any time before construction of an output end. This allows one process to resolve a name into a
NetChannelLocation
object and then pass this object on for another process to use in constructing the channel. The Channel Name Server will allow a channel to be registered multiple times with different names and/or in different name spaces. Channel implementations that make direct use of the Channel Name Server may forbid this, so the behaviour of channel implemenations should be checked before this is carried out- Author:
- Quickstone Technologies Limited
- See Also:
CNSService
,ServiceManager
,Node
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Field Summary
Fields Modifier and Type Field Description static java.lang.String
CNS_DEFAULT_SERVICE_NAME
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description static NetSharedChannelOutput
createAny2Net(java.lang.String name)
static NetSharedChannelOutput
createAny2Net(java.lang.String name, NameAccessLevel accessLevel)
static NetSharedChannelInput
createNet2Any(java.lang.String name)
static NetSharedChannelInput
createNet2Any(java.lang.String name, NameAccessLevel nameAccessLevel)
static NetAltingChannelInput
createNet2One(java.lang.String name)
static NetAltingChannelInput
createNet2One(java.lang.String name, NameAccessLevel nameAccessLevel)
static NetChannelOutput
createOne2Net(java.lang.String name)
static NetChannelOutput
createOne2Net(java.lang.String name, NameAccessLevel accessLevel)
static boolean
deregisterChannelName(java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey channelKey)
This deregisters a Channel name with the CNS.static void
destroyChannelEnd(NetChannelInput chanInEnd)
static void
destroyChannelEnd(NetChannelOutput chanOutEnd)
ServiceUserObject
getUserObject()
Returns anull
reference as this method has no use with this service.boolean
init(ServiceSettings settings)
This method does not need to be called for the Channel Name Server.static CNS
install(NodeKey key)
Installs and starts a Channel Name Server on the local Node.static CNS
install(NodeKey key, java.lang.String serviceName)
Installs and starts a Channel Name Server on the local Node.boolean
isRunning()
Returns whether the service is running.static ChannelNameKey
leaseChannelName(java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey channelKey)
static ChannelNameKey
register(NetChannelLocation ownerLocation, java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey key)
static ChannelNameKey
register(Networked owner, java.lang.String name)
static ChannelNameKey
register(Networked owner, java.lang.String name, ChannelNameKey key)
static ChannelNameKey
register(Networked owner, java.lang.String name, NameAccessLevel accessLevel)
static ChannelNameKey
register(Networked owner, java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey key)
static NetChannelLocation
resolve(java.lang.String name)
static NetChannelLocation
resolve(java.lang.String name, NameAccessLevel accessLevel)
void
run()
This defines the actions of the process.boolean
start()
This starts the channel name server.boolean
stop()
Stops the channel name server.
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Field Detail
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CNS_DEFAULT_SERVICE_NAME
public static final java.lang.String CNS_DEFAULT_SERVICE_NAME
- See Also:
- Constant Field Values
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Constructor Detail
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CNS
public CNS(NodeKey nodeKey) throws java.lang.IllegalStateException, java.lang.SecurityException
A public constructor which takes aNodeKey
as a parameter which should be the key for the local Node.- Parameters:
nodeKey
- aNodeKey
object that should match the local Node'sNodeKey
.- Throws:
java.lang.IllegalStateException
- if the local Node has not been initialized.java.lang.SecurityException
- if the suppliedNodeKey
object cannot be verified by the local Node.
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Method Detail
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start
public boolean start()
This starts the channel name server.
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stop
public boolean stop()
Stops the channel name server.
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init
public boolean init(ServiceSettings settings)
This method does not need to be called for the Channel Name Server. It returnstrue
.
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isRunning
public boolean isRunning()
Returns whether the service is running. At the moment this always returns false. This will probably change in the future. Early JCSP.NET applications always had the CNS process running in its own JVM.
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getUserObject
public ServiceUserObject getUserObject() throws java.lang.SecurityException
Returns anull
reference as this method has no use with this service.- Specified by:
getUserObject
in interfaceService
- Returns:
null
.- Throws:
java.lang.SecurityException
- if the calling Thread does not have access to the object.
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run
public void run()
Description copied from interface:CSProcess
This defines the actions of the process.
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resolve
public static NetChannelLocation resolve(java.lang.String name)
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resolve
public static NetChannelLocation resolve(java.lang.String name, NameAccessLevel accessLevel)
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register
public static ChannelNameKey register(Networked owner, java.lang.String name)
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register
public static ChannelNameKey register(Networked owner, java.lang.String name, NameAccessLevel accessLevel)
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register
public static ChannelNameKey register(Networked owner, java.lang.String name, ChannelNameKey key)
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register
public static ChannelNameKey register(Networked owner, java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey key)
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register
public static ChannelNameKey register(NetChannelLocation ownerLocation, java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey key)
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leaseChannelName
public static ChannelNameKey leaseChannelName(java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey channelKey) throws ChannelNameException, NameAccessLevelException
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deregisterChannelName
public static boolean deregisterChannelName(java.lang.String name, NameAccessLevel accessLevel, ChannelNameKey channelKey)
This deregisters a Channel name with the CNS. If the CNS Service is not running, this method will block until it is running. A boolean is returned to indicate whether deregistration was successful. This is also returned if the link to the CNS is lost.- Parameters:
name
- the name of the channel as a String.nameAccessLevel
- the nameAccessLevel of the channel.channelKey
- the ChannelNameKey to use to deregister the Channel name.- Returns:
- a boolean indicating success.
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createNet2One
public static NetAltingChannelInput createNet2One(java.lang.String name)
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createNet2One
public static NetAltingChannelInput createNet2One(java.lang.String name, NameAccessLevel nameAccessLevel)
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createNet2Any
public static NetSharedChannelInput createNet2Any(java.lang.String name)
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createNet2Any
public static NetSharedChannelInput createNet2Any(java.lang.String name, NameAccessLevel nameAccessLevel)
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createOne2Net
public static NetChannelOutput createOne2Net(java.lang.String name)
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createOne2Net
public static NetChannelOutput createOne2Net(java.lang.String name, NameAccessLevel accessLevel)
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createAny2Net
public static NetSharedChannelOutput createAny2Net(java.lang.String name)
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createAny2Net
public static NetSharedChannelOutput createAny2Net(java.lang.String name, NameAccessLevel accessLevel)
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destroyChannelEnd
public static void destroyChannelEnd(NetChannelInput chanInEnd)
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destroyChannelEnd
public static void destroyChannelEnd(NetChannelOutput chanOutEnd)
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install
public static CNS install(NodeKey key)
Installs and starts a Channel Name Server on the local Node. The service is installed with the default service name as specified byCNS.CNS_DEFAULT_SERVICE_NAME
. This method needs to be supplied with the local Node'sNodeKey
. This is required in order to obtain access to the Node's service manager.- Parameters:
key
- the local Node'sNodeKey
.- Returns:
- the
CNS
object installed. - Throws:
ServiceInstallationException
- if installation fails.
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install
public static CNS install(NodeKey key, java.lang.String serviceName)
Installs and starts a Channel Name Server on the local Node. The service is installed with the specified service name. This method needs to be supplied with the local Node'sNodeKey
. This is required in order to obtain access to the Node's service manager.- Parameters:
key
- the local Node'sNodeKey
.name
- the name to give the service.- Returns:
- the
CNS
object installed. - Throws:
ServiceInstallationException
- if installation fails.
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